As exemplified by U.S. Pat. No. 3,528,479, which is assigned to the assignee of the present invention, continuous casting apparatus has heretofore been devised which employs a rotatable wheel having an annular groove in the wheel rim into which molten metal is gravity fed. An endless band is mounted for movement along an endless path that extends over a portion of the wheel rim and groove to hold the molten metal in the groove as the wheel rotates. During rotation of the wheel and band the molten metal is cooled by water sprayed on the mold formed by the grooved casting wheel rim and band combination whereupon the metal solidifies. The casting is then stripped from the wheel in bar form at a point where the band in its endless travel leaves the casting wheel before it has rotated back to the point at which molten metal is being continuously gravity fed into the rim groove. The casting may then be fed to a rolling mill.
One persistant problem associated with the just described casting apparatus is that of the structural integrity and useful life of the endless band. This band, which typically is formed of hot rolled steel, is subjected to extremely high temperatures since it actually comes into contact with molten metal present within the casting wheel groove. However, it is only the central portion of the band that is brought into direct contact with the molten metal since the band side portions are in intimate sealing engagement with the wheel rim shoulders to each side of the rim groove. As water is sprayed onto the wheel and band to effect a cooling of the molten metal during wheel rotation, the wheel itself, including the two rim shoulders, are at a temperature substantially cooler than that of the solidifying molten metal. As a result the side portions of the band which overlay the wheel rim shoulders are similarly at a cooler temperature than that of the central portion. The band thus has a lateral temperature differential gradiant while in contact with the casting wheel which causes the central portion of the band to arch radially outwardly from the wheel upon thermal expansion rather than merely expand laterally. Since side portions of this arch overlay a portion of the rim shoulders adjacent the groove, some spacing between rim and band is created beside the groove into which molten metal may flow and form flashing during casting operations.
To prevent formation of this flashing a band hold-down roller has heretofore been located adjacent the point at which molten metal is gravity fed into the casting wheel groove. The band hold-down roller spring biases the metal band firmly against the wheel rim as it comes into initial contact with the rim whereupon the band forms a seal with the rim shoulder to each side of the groove. The just described solution to the problem of spacings forming over the rim shoulders has, unfortunately, led to the creation of a different problem. In forcing the arched metal band into intimate contact with the entire shoulder area of the casting wheel rim the cylindrical roller flattens the metallic band at this point along its endless travel. Once the band passes beyond the hold-down roller however it again assumes an arched configuration due to thermal expansion while it remains in contact with the molten metal within the wheel groove and therebeyond in its travel. Since here the molten metal is solidifying this re-arching of the band has not tended to result in any significant flow of the metal laterally onto the rim shoulders and form flashing. What does occur is a cyclically arching and flattening of the band under the alternating influences of thermal expansion and mechanical compression during each revolution of the band. This has resulted in rapid metal fatigue of the band necessitating frequent replacements.
In addition to rapid metal fatigue, some of the endless bands have also tended to slide or "walk" off of the idle and casting wheels due to excessive band camber. Those bands with significant camber will not maintain accurate alignment when rotated over the idle and casting wheel rims. It therefore is to these general problems which the present invention is primarily directed.